Iowa State University
Department of Physics and Astronomy
Erwin W. Fick Observatory
Ames, Iowa 50011
This report covers the period from September 2003
through August 2004. We limit the research descriptions in this report to brief summaries, along with specific internet addresses, and selected publications. For
more information on facilities, personnel, and research
programs, see our group website:
http://www.public.iastate.edu/∼astro
1
nior in physics or astronomy. The presentation material
is open for use by anyone:
http://www.polaris.iastate.edu
Kerton presented a talk at a special education session
of the May 2004 CASCA meeting. The talk detailed
the undergraduate lab course developed at ISU for nonscience students taking introductory astronomy classes.
Gonzalez and graduate student David Oesper have
signed a contract with Cambridge University Press to revise the textbook Observational Astronomy, by D. Scott
Birney. This project will be Oester’s Masters thesis
project. It is scheduled for completion in May 2005.
Prior to going out of print a few years ago, this was a
popular textbook for upper level undergraduate courses
on observational astronomy.
Personnel and Education
G. H. Bowen (emeritus), D. Carter-Lewis, J. Eitter (Observatory Manager), G. Gonzalez, S. Kawaler, C.
Kerton, F. Krennrich, R. Lamb (emeritus, resident in
Pasadena, CA), M. Pohl, C. Struck & L. A. Willson.
Graduate students in astronomy included J. Brown,
S. Hostler, A. Imran, B. Behera, M. Vuckovic, & Q.
Wang. During this period, S. Hostler completed a Masters degree and took a position with the SAO Submillimeter Array on Mauna Kea, and J. Brown completed a
Masters degree and entered the graduate program at the
University of New Mexico. D. Oesper progressed on a
Masters program that included astronomical pedagogy.
Stephane Lebohec completed his senior postdoctoral
fellowship working on SGARFACE and VERITAS, and
in August 2004 joined the faculty at the University of
Utah. Michael Daniel continues as a postdoctoral fellow
working on VERITAS and analysis of Whipple telescope
data. He is based in Ames, but makes frequent trips
to Arizona to observe or work on the VERITAS prototype telescope. Dirk Pützfeld is a postdoctoral scholar
working with M. Pohl.
Undergraduates involved in astronomical research
included ISU students G. Knoke, K. Marasinghe, A.
Marshall, and E. Potter; I. Radtke (Minnesota State
University, Mankato) joined us for summer research.
Kawaler continues as AURA member representative
for ISU and Director of the Whole Earth Telescope
(WET) collaboration. He also is serving a three-year
term as vice-president of I.A.U. Commission #27, and
serves on the AURA Solar Observatories Council. Reed
Riddle continued as Associate Director of Whole Earth
Telescope Operations, and in August moved to Caltech
where he is part of the TMT project. Pohl continues
as NASA Interdisciplinary Scientist for the GLAST mission. Willson serves Ex-President of the American Association of Variable Star Observers (AAVSO).
Willson, with several undergraduate and graduate
students, continue developing a series of web based astronomy modules (the Polaris Project). Aimed at the
freshman non-scientist, several modules have been tested
by students with backgrounds ranging from none to se-
2
Facilities
Gonzalez (with Eitter and Kerton) continued construction of a precision radial velocity spectrograph (m/s
resolution). The spectrograph is based on the “Externally Dispersed Interferometer” design of J. Ge and D.
Erskine. It will eventually be used with the Mather Telescope at Fick Observatory to obtain high precision radial
velocities to study giant planets around Sun-like stars.
CCD imaging and photometry at Fick Observatory,
with imaging on 84 nights over this period, and highspeed time series photometry of variable stars on 28 additional nights. These observations have employed the
Andor CCD camera; we are also developing a new system using a high-speed CCD photometer (based on the
Apogee AP-7) with custom software (designed by Riddle
and Radtke) to allow nearly real-time light curve analysis.
A new roof was installed on the movable roof of the
observatory. A new 8 1/2 foot Clear Skys Inc. dome
was installed around the 14” Celestron telescope used for
tours and the observing classes. A SBIG spectrometer
and CCD was also obtained for use with these classes.
3
3.1
Research Programs
Galaxies & ISM
Kerton, along with C. Brunt (UMass/FCRAO) and
L.B.G. Knee (HIA/NRC Canada) continued his studies of propagating star formation around small HII regions. In October 2003 he obtained new submm observations of a number of HII regions using SCUBA on
JCMT. The science program is now moving towards using deep NIR imaging to investigate the embedded stellar
content in more detail while awaiting the arrival of the
SCUBA2 instrument on JCMT to continue the submm
1
survey observations. A poster reviewing the JCMT observations was presented at the Canadian Astronomical
Society (CASCA) annual meeting in May 2004.
Kerton continues his studies on the ISM as part of
the International Galactic Plane Survey (IGPS). From
May-August 2004 two undergraduate students worked
on IGPS related projects. J. Wahl (UNI) constructed
an observational database of the Cepheus star-forming
region and S. Dennis (ISU) worked on a catalog of extended 1420 MHz emission features seen in IGPS data.
Kerton is investigating HI self-absorption features seen
in the IGPS data and is particularly interested in the
rare cases where the cold HI is seen both in emission
and absorption.
As part of his involvment with the Galactic Arecibo
L-Band Feed Array (GALFA) consortium Kerton is looking at high velocity HI features seen in IGPS data with
the goal of characterizing their frequency and association
with known massive star forming regions. Such low intensity, high-velocity wings seen in older HI surveys are
thought to be associated with old supernova remnants
and are a proposed target for future ALFA observations.
Kerton continues to work on the creation of highresolution IRAS-based maps of the Galactic plane. These
maps are integrated into the IGPS data base and provide
information on the dust component of the ISM at a comparable resolution to the radio wavelength surveys. The
final data products are also being made available through
the Infrared Science Archive (IRSA) ATLAS web site
C. Struck continued work on models of star–gas dynamics and induced star formation in pre-merger stages
of galaxy collisions. This work focuses on modeling specific well observed systems. A talk on the importance of
detailed studies of specific systems (given at IAU Symposium 217) was published in this period. A Chandra
Observatory X-ray study of the classic starburst system
Arp 284, reporting the discovery of an incipient wind
and several ultraluminous sources associated with tidal
structures, has been submitted for publication in the AJ.
Guest observer time was obtained with a number of collaborators to study systems with bridges and tails with
the Spitzer Space Telescope and GALEX, and to study
ring galaxies with GALEX. These observations should
give unprecedented information about star formation in
collisionally induced waves in galaxies. See
http://www.public.iastate.edu/∼curt.
3.2
dence of early life on Earth, exploring the possibility of
re-seeding the Earth following a sterilizing impact, and
search strategies for Terran meteorites on the Moon.
Struck, Willson and Cohanim (former undergrad.)
completed work on the effects of accretion onto giant
planets and brown dwarfs orbiting in the extended atmospheres and winds of stars like the Sun in their
late evolutionary stages (AGB, Mira phase). A grid of
two-dimensional numerical models highlighting the bow
shock, wake and accretion hydrodynamics of such systems, was published in the MNRAS. Related material
can be found at;
http://www.public.iastate.edu/∼lwillson
Struck, Willson, Bowen and former graduate students D. C. Smith and G. Turner also completed and
published analytic models of the self-similar structure of
the winds of long-period variables. In the case of pulsationally driven winds the models are based on nonbarotropic, Reynolds-type equations, like those used in
turbulence studies. The work also suggests that dustdriven winds are self-regulated.
Willson spent the academic year on “faculty professional development assignment,” visiting the astronomy
department at the University of Minnesota, the HarvardSmithsonian Center for Astrophysics, Uppsala University, and UC Berkeley. Her research focused on (a) understanding the implications of the realization that Miras are surrounded by material with a large amount of
water vapor near two stellar radii (Traub et al. in prep);
(b) considering possible explanations for variations in the
periods of Miras over decadal timescales (Templeton et
al in prep); and (c) exploring with C. Struck the effects
of episodic mass loss on orbits. Her main project for
the year was beginning to write a new textbook, Essential Physics of Stellar and Planetary Atmospheres, under
contract with Cambridge U. Press. In conjunction with
that project she gave a seminar series at the University of Minnesota. She also gave talks at all the above
listed institutions plus the University of Washington and
Stockholm University on her research. Finally, she spent
some time at the American Association of Variable Star
Observers while director Janet Mattei was ill, and served
on the search committee for a new director.
A new flare star, discovered by Eitter, is being monitored which was first seen on some wide field observations of comet Ikeya-Zhang in 2002. Observations of a
21.45 hour eclipsing binary discovered by Mike McClure
are being taken. Mike is a ISU physics alumnus who is
an amateur astronomer searching for new variable stars.
Under Kawaler’s direction, the Whole Earth Telescope continued reduction and analysis of data from
prior campaigns, including the August 2003 campaign
on the pulsating sdB star KPD 1930. With undergraduate L. Potter, Kawaler and the collaboration completed analysis of the pulsating hot white dwarf PG
1707+427. In addition, the WET collaboration began
preparations for the 24th WET campaign, scheduled for
October 2004. Graduate student S. Hostler completed
her Masters research project with analysis of 20+ years
Stars and Planets
Gonzalez continues a long-term program, started in
late 1995, to derive the basic properties of stars with
planets. This is the Ph.D. thesis topic of C. Laws (U.
Washington), which he expects to complete in December 2004. Work with G. Wallerstein (U. Washington)
and S. Giridhar (Indian Inst. of Astrophysics) on the
abundances of very metal-poor cool giants continues; the
work is based on observations obtained in 2000 and 2001
with the KPNO 4-m and Apache Point 3.5-m telescopes.
In collaboration with J. Armstrong (Weber State), Gonzalez continues a study of the Moon as a source for evi2
of data on the pulsating white dwarf G29-38, including
data from the 23rd WET campaign and data taken locally at Fick Observatory.
On the theoretical side, Kawaler and graduate student Hostler completed their initial study of the evolution of angular momentum within stars as the evolved
from the main sequence to the white dwarf (and hot subdwarf) phases. Results of these studies suggest new ways
of analyzing the pulsating members of those classes to
look for evidence of rapid core rotation. Other theoretical studies include collaborative work on the influence
of neutrinos on the evolution of DB white dwarfs, and
topics in pulsations of Miras and semiregular variables.
For more details about work in these areas, as well
as links to the Whole Earth Telescope project and
Kawaler’s teaching activities, see
http://www.public.iastate.edu/∼sdk
3.3
ods for best utilizing this array, particularly in regard to
obtaining the lowest energy threshold. This work utilizes
Monte Carlo code largely developed here.
TeV science issues being addressed at ISU include
the measurement of energy spectra of AGN, the implications for particle acceleration in the vicinity of supermassive black holes, and implications for extra-galactic
background light. Primary science results from last year
include a significant new analysis of joint constraints on
blazar TeV and EBL by Dwek and Krennrich, spectral
analysis of the blazars H1426+426 and 1ES1959+650
and a search for TeV gamma rays from M87. Details
are summarized in the publication list below.
In addition we have developed a unique trigger system (SGARFACE) now attached to the Whipple telescope to search for burst phenomena on timescales of
10 nanoseconds to 10 microseconds. Frank Krennrich,
Stephan Lebohec and Bagmeet Beherra are working on
the first data and developing data analysis techniques.
SGARFACE will eventually be expanded and moved to
VERITAS.
Particle Astrophysics
Faculty members Frank Krennrich and David CarterLewis work entirely in this area. Martin Pohl divides
his time between GLAST (satellite/GeV energies) and
VERITAS (ground-based/TeV energies).
3.3.1
3.3.2
High Energy Astrophysics
Pohl continues his investigations of high–energy phenomena in supernova remnants, AGNs, and the Universe.
An origin of cosmic rays in supernova remnants
(SNR) would have profound consequences for how these
particles would be distributed in the Galaxy, and consequently how the local cosmic-ray measurements have to
be interpreted. The effects are possibly visible in the
spectra of diffuse galactic γ-ray emission, where they
could account for observed excess emission at a few GeV.
In particular the flux of high-energy electrons would
have a highly inhomogeneous distribution in the galactic disk, and it would also display temporal variations.
The typical correlation length for the spatial fluctuations
in the electron flux is approximately 200 pc at an electron energy of 100 GeV or higher. The distribution of
cosmic-ray nucleons would show fluctuation at the 20%
level with occasional spikes of much higher amplitude,
which would only be observed for primary cosmic rays.
Therefore the commonly used method of determining CR
propagation parameters by fitting secondary-to-primary
ratios appears flawed on account of the variations that
these ratios would show throughout the Galaxy.
Three shell-type SNRs have been detected at TeVscale γ-ray energies to date, all of which show nonthermal X-ray emission, which presumably is synchrotron
radiation. A large fraction of the non-thermal X-ray
emission originates from very thin filaments, which are
probably magnetic structures at the contact discontinuity between the ejecta and the circumstellar material, suggesting that the radiating relativistic electrons
are not accelerated at the forward shock and hence not
produced by the commonly assumed process of diffusive
shock acceleration.
Active galactic nuclei (AGNs) are powerful sources
with relativistic outflows that can emit the bulk of their
TeV Gamma-ray Astronomy
Ground-based gamma-ray astronomy has opened up
a new observational window for observing TeV (1012 eV)
photons from active galactic nuclei (AGN), supernova
remnants and pulsars. Our group, as part of the Whipple
collaboration has pioneered the technique of detecting
gamma-rays from using large (Whipple 10 m), groundbased optical telescopes.
Astrophysics at TeV energies is about to undergo a
revolution as the next generation Cherenkov telescopes
(VERITAS, HESS, MAGIC, CANGAROO) come on
line. The existence of several types of cosmic accelerators emitting TeV gamma rays is well established; the
underlying physics is not. These new arrays will have
1-2 orders of magnitude better sensitivity, increased angular resolution and sensitivity extending to dramatically lower energies. In addition the GLAST satellite
will give unprecedented sensitivity at GeV energies overlapping (or almost overlapping) with the low energies of
the Cherenkov arrays.
The VERITAS array (Very Energetic Radiation Imaging Telescope Array System) is the successor of the
Whipple telescope and will have dramatically improved
sensitivity, energy threshold, and angular and energy
resolution. At ISU, we have designed and are building the focus boxes and focal plane instrumentation for
this array. The first telescope is now functioning with a
subset of pixels at Whipple Observatory basecamp near
Amado Arizona. (The VERITAS array will eventually
be located at KPNO.) The remaining photomultipliertube/preamp assemblies for the first telescope have now
been completed at ISU, and the camera will soon have
a full complement of 499 pixels.
With Stephan LeBohec (Utah) and Charles Duke
(Grinnell), we are presently investigating analysis meth3
luminosity in the form of gamma rays, the flux of which
displays variability on time scales so short that, on account of causality, the emission regions can not be larger
than a few light hours.
Relativistic collision fronts in the jets of AGN make
excellent candidates for hosting the very rapid acceleration processes, that are required to explain the fast variability observed from AGN. A kinetic treatment of the
relativistic collision fronts is desirable on account of the
collisionless nature of astrophysical plasmas. We have
developed the ”relativistic pick-up model”, in the framework of which the individual TeV flares can be explained
as the consequence of the collisionless interaction of a single massive outflow component with an inhomogeneous
ambient medium.
The predicted radiation reproduces the observed
multi-band spectra and the lightcurves of gamma-ray
blazars while making definite predictions for the neutrino
emission. Corresponding calculations are being made for
outflows consisting of an e+ /e− pair plasma, which is
possibly the case in gamma-ray bursts.
A host of data is available to date that allows tests of
cosmological models. We investigate possible extensions
and generalizations of the simple Friedmann-Lemâitre
universes by using statistical tests on a sample of radio
galaxies and galaxy clusters. We find that one class of
non-Riemannian structure can not contribute more than
5% of the critical mass in the universe.
For further information about Pohl’s research programs, see
http://cherenkov.physics.iastate.edu/∼mkpohl
B.G. Castanheira, et al. (including S.D. Kawaler) (the
WET collaboration) 2004, “Observations of the Pulsating White Dwarf G 185-32,” A&A, 413, 623.
M.K. Daniel, et al., (including D. A. Carter-Lewis,
F. Krennrich, & S. LeBohec) 2004, “The energy
spectrum of the BL Lac object 1ES1959+650,” ApJ,
in press.
I.C. De La Calle Perez, et al. (including D.A. CarterLewis, M.K. Daniel, F. Krennrich, & S. Le
Bohec) 2004, “Search for high energy gamma rays
from an X-Ray selected blazar sample,” ApJ, 599,
909.
E. Dwek & F. Krennrich 2004, “Simultaneous constraints on the spectrum of the extragalactic background light and the intrinsic TeV spectra of Mrk
421, Mrk 501 and H1426+428,” ApJ, in press.
A. Falcone, et al., (including D. A. Carter-Lewis,
F. Krennrich, & S. LeBohec) 2004, “A search
for TeV gamma-Ray emission from high-peaked flat
spectrum radio quasars using the Whipple air-Cherenkov
telescope,” ApJ, in press.
D. Geisler, V. V. Smith, G. Wallerstein, G. Gonzalez,
& C. Charbonnel, 2004, “’Sculptor’-ing the Galaxy?
The chemical compositions of red giants in the Sculptor dwarf spheroidal galaxy,” AJ, in press.
T.A. Hall, et al. (including D.A. Carter-Lewis, F.
Krennrich, & S. Le Bohec) 2003, “Search for TeV
emissions from pulsars in binary systems,” ApJ, 583,
853.
J. Holder, et al. (including D.A. Carter-Lewis, F.
Krennrich, S. Le Bohec, & D. Petry) 2003,
“TeV gamma rays from the BL Lacertae Object 1ES
1959+650 with the Whipple 10 Meter Telescope,”
ApJ, 583, L9.
PUBLICATIONS
F. Aharonian, et al. (including M. Pohl) 2004, “H.E.S.S.
observations of PKS 2155-304,” A&A, submitted
F. Aharonian, et al. (including M. Pohl) 2004, “Calibration of cameras of the H.E.S.S. detector,” Astropart. Phys., in press
D. Horan, et al. (including D.A. Carter-Lewis, M.K.
Daniel, F. Krennrich, & S. Le Bohec) 2004,
“Constraints on the Very High Energy Emission from
BL Lacertae Objects,” ApJ, 603, 51.
F. Aharonian, et al. (including M. Pohl) 2004, “Very
high energy gamma-rays from the direction of Sagittarius A∗ ,” A&A 425, L13
U. Hwang et al. (including M. Pohl) 2004, “A million
second Chandra view of Cassiopeia A,” ApJ, submitted
C. Akerlof, et al. (including D. A. Carter-Lewis &
F. Krennrich) 2003, “A search for correleations
of TeV gamma-rays with ultra-high energy cosmic
rays,” ApJ, 586, 1232.
I. I. Ivans, C. Sneden, G. Wallerstein, R. P. Kraft, J.
E. Norris, J. P. Fulbright, & G. Gonzalez 2004,
“On the Question of a Metallicity Spread in Globular
C. Arbeiter, M. Pohl, & R. Schlickeiser 2004, “SynchrotronCluster M22 (NGC 6656),” MnSAI, 75, 286.
self-comptonization in a relativistic collision front
S.D. Kawaler, E. Potter, M. Vuckovic, et al. (the
model,” ApJ, submitted
WET collaboration) 2004, “Whole Earth Telescope
I. Büsching, A. Kopp, M. Pohl, R. Schlickeiser, C. Perobservations of the pulsating hot white dwarf PG
rot, & I. Grenier 2004 “Cosmic-ray propagation prop1707+427,” A&A, in press.
erties for an origin in SNRs,” ApJ, in press
S. D. Kawaler & S.R. Hostler 2004, “Internal Rotation of Subdwarf B Stars: Limiting Cases and Asteroseismological Consequences,” ApJ, submitted.
Y.M. Butt, P. Benaglia, J.A. Combi, M. Corcoran, T.M.
Dame, J. Drake, M. Kaufman Bernadó, P. Milne,
F. Miniati, F., M. Pohl, O. Reimer, G.E. Romero,
& M. Rupen, 2003, “CHANDRA/VLA follow-up of
TeV J2032+4131, the only unidentified TeV gammaray source,” ApJ, 597, 494.
C.R. Kerton 2004, “A direct determination of the spin
temperature of an HI self-absorption feature,” ApJ,
in press
4
C.R. Kerton, C.M. Brunt, & L.B.G. Knee 2003, “High
Spatial Dynamic Range HI Surveys of Nearby Molecular Cloud Complexes,” in Milky Way Surveys: The
Structure and Evolution of Our Galaxy, ASP Conf.
Ser. 317 (available October 2004)
M.D. Reed, S.D. Kawaler, et al. (the WET collaboration) 2004, “The long term pulsational stability of
the pulsating sdB star Feige 48”, MNRAS, 348, 1164.
O. Reimer, M. Pohl, P. Sreekumar, & J.R. Mattox 2003,
“EGRET upper limits on the high-energy gamma-ray
emission of galaxy clusters,” ApJ, 588, 155
C.R. Kerton, C.M. Brunt, & and R. Kothes 2004, “The
overlooked HII region DA 568,” AJ, 127, 1059
R. Schlickeiser, M. Pohl, & R. Vainio 2003, “The influence of electron impact ionisation in the relativistic
pick-up of interstellar neutrals,” ApJ, 596, 840
C. R. Kerton, C.M. Brunt, C.E. Jones, & S. Basu 2003,
“On the intrinsic shape of molecular clouds,” A&A,
411, 149
M. Siewert, M. Pohl, & R. Schlickeiser, R. 2004, “The
impact of thermal gas in AGN jets on the lowfrequency emission,” A&A 425, 405
C. R. Kerton, G. Cameron, D. Oesper, & L.A.
Willson 2004, “Integrating a Lab Experience with
an Astro 101 Class,” in Physics in Canada, Vol. 60,
No. 3, May-June 2004, 58 (abstract)
B. J. Smith, C. Struck, & M. Nowak 2004, “Chandra
X-ray Imaging of the Interacting Starburst Galaxy
System NGC 7714/15: Tidal ULXs, Emergent Wind,
and Resolved HII Regions,”, AJ, submitted.
C.R. Kerton, L.B.G. Knee, & C.M. Brunt 2004, “Propagating Star Formation Around Single O star HII
Regions,” in Physics in Canada, Vol. 60, No. 3,
May-June 2004, 132 (abstract)
C. Struck 2004, “Case Studies of Mass Transfer and
Star Formation in Galaxy Collisions,” in Recycling
Intergalactic and Interstellar Matter: IAU Symposium Series, Vol. 217, eds. P.-A. Duc, J. Braine, &
E. Brinks (San Francisco: ASP), p 400.
D. Kilkenny, M.D. Reed, D. O’Donoghue, S.D. Kawaler
et al. (the WET collab.) 2003 “A Whole Earth Telescope campaign on the pulsating subdwarf B binary
system PG 1336-018 (NY Vir)”, MNRAS, 345, 834.
C. Struck, B. E. Cohanim, & L. A. Willson 2004,
“Continuous and Burst-like Accretion on to Substellar Companions in Mira Winds,” MNRAS, 347, 173.
F. Krennrich, et al. (including D. A. Carter-Lewis,
M. K. Daniel, & S. LeBohec 2004, “VERITAS:
the Very Energetic Radiation Imaging Telescope Array System,” New Astronomy Reviews, 48, 345.
C. Struck, D. C. Smith, L. A. Willson, G. Turner, & G.
H. Bowen 2004, “The Self-Regulated Winds of LongPeriod Variable Stars,” MNRAS, 353, 559.
K. Kosak, et al. (including D.A. Carter-Lewis, M.K.
Daniel, F. Krennrich, & S. Le Bohec) 2004,
“TeV Gamma-Ray Observations of the Galactic Center,” ApJ, 608, L97.
G. Tautvaisiene, G. Wallerstein, D. Geisler, G. Gonzalez, & C. Charbonnel 2004, “Elemental abundances
of three red giants in Terz. 7, a globular cluster associated with the Sagittarius galaxy,” AJ, 127, 373.
C. Laws, G. Gonzalez , et al., 2003, “Fossils in the Photosphere: Condensation Temperature Trends in the
Chemical Abundances of Stars with Radial-Velocity
Companions,” BAAS, 203, #6.07.
R. Vainio, M. Pohl, & R. Schlickeiser 2004, “Conversion
of bulk kinetic energy into radiation in AGNs and
GRBs: particle transport effects,” A&A, 414, 463
S. Le Bohec, et al. (including D. A. Carter-Lewis,
M.K. Daniel, & F. Krennrich) 2004, “Observations of M87 at E ¿ 400 GeV with the Whipple 10m
Telescope,” ApJ, 610, 156.
D.E. Winget, D.J. Sullivan, T.S. Metcalfe, S.D. Kawaler,
& M.H. Montgomery 2004, “A strong test of electroweak theory using pulsating DB white dwarf stars as
plasmon neutrino detectors,” ApJ, 602, L109.
M. Lyutikov & M. Pohl 2004, “The origin of nonthermal X-ray filaments and TeV emission in young
SNRs,” ApJ, 609, 785
P.R. Wood, E.A. Olivier, & S. D. Kawaler 2004, “Long
Secondary Periods in Pulsating Asymptotic Giant
Branch Stars: An Investigation of their Origin”, ApJ,
604, 800.
T.S. Metcalfe, M.H. Montgomery, & S. D. Kawaler
2003 , “Probing the envelope structure of DBV white
dwarfs”, MNRAS, 344, L88.
Steven D. Kawaler
A. Mukudam, et al. (the WET collaboration, including
S.D. Kawaler) 2004, “Constraining the Evolution of
ZZ Ceti”, ApJ, 594, 961.
M. Pohl, C. Perrot, I. Grenier, & S. Digel 2003, “The
imprint of Gould’s Belt on the local cosmic-ray electron spectrum,” A&A, 409, 581
D. Pützfeld, M. Pohl, & Z.-H. Zhu, Z.-H. 2004, “Complementary constraints from FR IIb radio galaxies
and X-ray gas mass fractions in clusters on nonstandard cosmological models,” ApJ, submitted
5